Burned out coil and points after leaving ignition on

I just heard back from the company that is installing a new stereo in my ice cream truck and they told me that they can't start the truck. I just brought them the truck from a mechanic that has been working on it for months and I drove it there without a problem. The mechanic went to the stereo place and told them that because they left the ignition on, it burned out the coil and the points on the distributer which is why the engine wasn't getting any spark. Is this a valid reason or is it possible the distributor that was installed was faulty or installed improperly? There is a growing dispute over who is at fault and who should cover the cost of the tow back to the original shop and the repairs needed.